Dual gate control for trench shaped thin film transistors

ABSTRACT

Disclosed herein are dual gate trench shaped thin film transistors and related methods and devices. Exemplary thin film transistor structures include a non-planar semiconductor material layer having a first portion extending laterally over a first gate dielectric layer, which is over a first gate electrode structure, and a second portion extending along a trench over the first gate dielectric layer, a second gate electrode structure at least partially within the trench, and a second gate dielectric layer between the second gate electrode structure and the first portion.

BACKGROUND

Thin film transistors (TFT) include a thin film or films of an activesemiconductor layer, a gate dielectric separating a gate electrode fromthe active semiconductor layer, and metallic contacts coupled to theactive semiconductor layer over a supporting substrate. TFTs may becontrasted with conventional transistors where the semiconductormaterial typically is the substrate and/or where the semiconductormaterial is a crystalline material. TFTs are useful in a variety ofcontexts including thin film electronics, displays, and embedded memorysuch as embedded dynamic random access memory (eDRAM).

As such, there is a continuing need for improved TFTs. Such improvementsmay become critical as the desire to implement TFTs in eDRAM as well asin other applications becomes more widespread.

BRIEF DESCRIPTION OF THE DRAWINGS

The material described herein is illustrated by way of example and notby way of limitation in the accompanying figures. For simplicity andclarity of illustration, elements illustrated in the figures are notnecessarily drawn to scale. For example, the dimensions of some elementsmay be exaggerated relative to other elements for clarity. Further,where considered appropriate, reference labels have been repeated amongthe figures to indicate corresponding or analogous elements. In thefigures:

FIG. 1A illustrates a cross-sectional view of an example thin filmtransistor structure;

FIG. 1B illustrates a top-down view of the thin film transistorstructure of FIG. 1A;

FIG. 2A illustrates a cross-sectional view of another example thin filmtransistor structure;

FIG. 2B illustrates a top-down view of the thin film transistorstructure of FIG. 2A;

FIG. 3 illustrates a flow diagram illustrating an example process forfabricating thin film transistor structures;

FIGS. 4, 5, 6A, 7A, 8, 9, 10, 11, 12, 13, 14, 15, 16, and 17A illustratecross-sectional side views of example thin film transistor structures asparticular fabrication operations are performed;

FIGS. 6B, 7B, and 17B illustrate top-down views of the thin filmtransistor structures of FIGS. 6A, 7A, and 17A, respectively;

FIG. 18 illustrates a flow diagram illustrating an example process forfabricating thin film transistor structures;

FIGS. 19, 20, 21, and 22A illustrate cross-sectional side views ofexample thin film transistor structures as particular fabricationoperations are performed;

FIG. 22B illustrates a top-down view of the thin film transistorstructure of FIG. 22A;

FIG. 23 illustrates a cross-sectional side view of a memory devicestructure;

FIG. 24 illustrates a mobile computing platform and a data servermachine employing memory devices including dual gate trench shaped thinfilm transistors; and

FIG. 25 is a functional block diagram of an electronic computing device,all arranged in accordance with at least some implementations of thepresent disclosure.

DETAILED DESCRIPTION

One or more embodiments or implementations are now described withreference to the enclosed figures. While specific configurations andarrangements are discussed, it should be understood that this is donefor illustrative purposes only. Persons skilled in the relevant art willrecognize that other configurations and arrangements may be employedwithout departing from the spirit and scope of the description. It willbe apparent to those skilled in the relevant art that techniques and/orarrangements described herein may also be employed in a variety of othersystems and applications other than what is described herein.

Reference is made in the following detailed description to theaccompanying drawings, which form a part hereof, wherein like numeralsmay designate like parts throughout to indicate corresponding oranalogous elements. It will be appreciated that for simplicity and/orclarity of illustration, elements illustrated in the figures have notnecessarily been drawn to scale. For example, the dimensions of some ofthe elements may be exaggerated relative to other elements for clarity.Further, it is to be understood that other embodiments may be utilizedand structural and/or logical changes may be made without departing fromthe scope of claimed subject matter. It should also be noted thatdirections and references, for example, up, down, top, bottom, over,under, and so on, may be used to facilitate the discussion of thedrawings and embodiments and are not intended to restrict theapplication of claimed subject matter. Therefore, the following detaileddescription is not to be taken in a limiting sense and the scope ofclaimed subject matter defined by the appended claims and theirequivalents.

In the following description, numerous details are set forth. However,it will be apparent to one skilled in the art, that the presentinvention may be practiced without these specific details. In someinstances, well-known methods and devices are shown in block diagramform, rather than in detail, to avoid obscuring the present invention.Reference throughout this specification to “an embodiment” or “oneembodiment” means that a particular feature, structure, function, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. Thus, the appearances ofthe phrase “in an embodiment” or “in one embodiment” in various placesthroughout this specification are not necessarily referring to the sameembodiment of the invention. Furthermore, the particular features,structures, functions, or characteristics may be combined in anysuitable manner in one or more embodiments. For example, a firstembodiment may be combined with a second embodiment anywhere theparticular features, structures, functions, or characteristicsassociated with the two embodiments are not mutually exclusive. As usedin the description of the invention and the appended claims, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willalso be understood that the term “and/or” as used herein refers to andencompasses any and all possible combinations of one or more of theassociated listed items.

The terms “coupled” and “connected,” along with their derivatives, maybe used herein to describe structural relationships between components.It should be understood that these terms are not intended as synonymsfor each other. Rather, in particular embodiments, “connected” may beused to indicate that two or more elements are in direct physical orelectrical contact with each other. “Coupled” may be used to indicatethat two or more elements are in either direct or indirect (with otherintervening elements between them) physical or electrical contact witheach other, and/or that the two or more elements co-operate or interactwith each other (e.g., as in a cause an effect relationship). The term“adjacent” here generally refers to a position of a thing being next to(e.g., immediately next to or close to with one or more things betweenthem) or adjoining another thing (e.g., abutting it).

The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,”“under,” and the like in the description and in the claims, if any, areused for descriptive purposes and not necessarily for describingpermanent relative positions. For example, the terms “over,” “under,”“front side,” “back side,” “top,” “bottom,” “over,” “under,” and “on” asused herein refer to a relative position of one component, structure, ormaterial with respect to other referenced components, structures ormaterials within a device, where such physical relationships arenoteworthy. These terms are employed herein for descriptive purposesonly and predominantly within the context of a device z-axis andtherefore may be relative to an orientation of a device. Hence, a firstmaterial “over” a second material in the context of a figure providedherein may also be “under” the second material if the device is orientedupside-down relative to the context of the figure provided. In thecontext of materials, one material disposed over or under another may bedirectly in contact or may have one or more intervening materials.Moreover, one material disposed between two materials may be directly incontact with the two layers or may have one or more intervening layers.In contrast, a first material “on” a second material is in directcontact with that second material. Similar distinctions are to be madein the context of component assemblies. The term “between” may beemployed in the context of the z-axis, x-axis or y-axis of a device. Amaterial that is between two other materials may be in contact with oneor both of those materials, or it may be separated from both of theother two materials by one or more intervening materials. A material“between” two other materials may therefore be in contact with either ofthe other two materials, or it may be coupled to the other two materialsthrough an intervening material. A device that is between two otherdevices may be directly connected to one or both of those devices, or itmay be separated from both of the other two devices by one or moreintervening devices.

The terms “substantially,” “close,” “approximately,” “near,” and“about,” generally refer to being within +/−10% of a target value. Forexample, unless otherwise specified in the explicit context of theiruse, the terms “substantially equal,” “about equal” and “approximatelyequal” mean that there is no more than incidental variation betweenamong things so described. In the art, such variation is typically nomore than +1-10% of a predetermined target value. Unless otherwisespecified the use of the ordinal adjectives “first,” “second,” and“third,” etc., to describe a common object, merely indicate thatdifferent instances of like objects are being referred to, and are notintended to imply that the objects so described must be in a givensequence, either temporally, spatially, in ranking or in any othermanner The term layer as used herein may include a single material ormultiple materials. As used in throughout this description, and in theclaims, a list of items joined by the term “at least one of” or “one ormore of” can mean any combination of the listed terms. For example, thephrase “at least one of A, B or C” can mean A; B; C; A and B; A and C; Band C; or A, B and C.

Semiconductor device structures, devices, apparatuses, computingplatforms, and methods are described below related to dual gate thinfilm transistors.

As described above, it may be advantageous to provide improved thin filmtransistor (TFT) structures. In an embodiment, a TFT structure includesa non-planar semiconductor TFT layer. As used herein, a semiconductorTFT layer or simply semiconductor layer may include any suitablesemiconductor thin film such as an amorphous or polycrystallinesemiconductor material. A polycrystalline material includes any materialhaving micro-scale or nano-scale crystal grains and includenanocrystalline materials. For example, nanocrystalline materialsinclude materials having crystallites that are not larger than 5 nm(e.g., 0.5 to 5 nm in cross sectional length). An amorphous material maybe any material that lacks long range order (e.g., has no structuralorder) and includes interconnected material blocks. As discussed, thenon-planar semiconductor TFT layer is non-planar. As used herein, theterm non-planar refers to any layer having one or more non-planarsurfaces such that the surface deviates from a particular plane. Thetern non-planar as used herein indicates one or more portions of thenon-planar layer are substantially out of plane with respect to otherportions and may be contrasted with substantially planar surfaces thatare merely not perfectly planar. For example, a non-planar semiconductorTFT layer may include a first portion over a first gate dielectric layerand a second portion conformal to one or more sidewalls of a trenchwithin a patterned layer such that the patterned layer is adjacent tothe first gate dielectric layer and the non-planar layer. For example, asurface of the first gate dielectric layer and the sidewall(s) of thetrench may be at an angle with respect to one another such assubstantially orthogonal or the like. For example, such a TFT structuremay be characterized as a trench-type TFT structure as the non-planarsemiconductor layer conforms to a trench.

As discussed, a first portion of the non-planar semiconductor TFT layermaybe over a first gate dielectric layer. A first gate electrodestructure may be adjacent the first gate dielectric layer and oppositethe first portion such that the first gate electrode structure maycontrol (e.g., exert an electric field on) the first portion of thenon-planar semiconductor TFT layer.

Furthermore, at least a portion of a second gate electrode structure maybe in the trench of the patterned layer and adjacent to the firstportion of the non-planar semiconductor TFT layer such that a secondgate dielectric layer is between the first portion and the second gateelectrode structure. Thereby the first gate electrode may also control(e.g., exert an electric field on) the first portion of the non-planarsemiconductor TFT layer. As used herein, the term in or within a trenchindicates that the structure is at least partially below or within asurface that would define a boundary of the trench. For example, thesurface defining a boundary of a trench extends to connect top edges ofsidewalls of the trench. A body that is at least partially in a trenchhas a portion thereof that extends into the trench across that boundary,either partially or entirely (e.g., the body may be partially orentirely within the trench). The TFT structure may further include asource and a drain coupled to the non-planar semiconductor TFT layer.

Such TFT structures provide dual gate control via the first and secondgate electrode structures. The first and second gate electrodestructures may be integrated such that the same control (e.g., controlsignal, switching signal, bias, etc.) is provided via the two gateelectrode structures or they may be separate such that different controlis provided by the first gate electrode structure with respect to thesecond gate electrode structure. Such dual gate architectures providefor advantageous control and operational characteristics of non-planaror trench-type TFT structures. For example, dual gate electrodestructures (e.g., dual gates) provide for improved short channel controlwhile maintaining low contact resistance and low parasitic gate tosource/drain coupling capacitance. For example, the source to drainpathway for non-planar or trench-type TFT structures is longer toprovide improved gate control using a second gate. Furthermore,non-planar or trench-type TFT structures provide improved density withrespect to planar TFT structures and improved performance as devicedensity increases. For example, non-planar or trench-type TFT structuresprovide increased effective gate lengths without increasing the lateralfootprint of the TFT.

As discussed, a second gate electrode structure extends within a trenchand adjacent to a first portion of the non-planar semiconductor TFTlayer. For example, the second gate electrode structure extends alongthe non-planar semiconductor TFT layer on the sidewall of the patternedlayer defining the trench. The second gate electrode structure mayinclude a portion of the second gate dielectric layer on a sidewall ofthe second gate electrode. In some embodiments, a dielectric spacerlayer is provided between the non-planar semiconductor TFT layer on thesidewall and the second gate dielectric layer. Such embodiments providefor lower capacitance coupling from the source/drain to the gate.Furthermore, such embodiments may provide doping of the non-planarsemiconductor TFT layer via the dielectric spacer layer. In otherembodiments, a portion of the source and a portion of the drain areprovided between the non-planar semiconductor TFT layer and the secondgate dielectric layer. Such embodiments provide for lower contactresistances and maximized overlap for contact area to improve drivecurrent.

FIG. 1A illustrates a cross-sectional view of an example thin filmtransistor structure 100 and FIG. 1B is a top-down view of thin filmtransistor structure 100, arranged in accordance with at least someimplementations of the present disclosure. As shown, FIG. 1A provides across-sectional view along an x-z plane and FIG. 1B provides a top-downview along the A-plane in FIG. 1A (e.g., along an x-y plane). Asillustrated, the x-y plane may be in-plane, in-line, or the like withrespect to a lateral direction of thin film transistor structure 100 andthe z-direction may be perpendicular with respect to the lateraldirection of thin film transistor structure 100.

As shown, thin film transistor structure 100 may include a substrate101, a gate electrode structure 102, a gate dielectric layer 103, apatterned layer 104, a non-planar semiconductor layer 105, a sidewallspacer 106, a gate dielectric layer 107, a gate electrode structure 108,a source 109, and a drain 110. Notably, thin film transistor structure100 includes a dual gate architecture including gate electrode structure102, gate dielectric layer 103, gate dielectric layer 107, and gateelectrode structure 108. For example, a portion of non-planarsemiconductor layer 105 acts as a semiconductor channel for thin filmtransistor structure 100. In some embodiments, gate electrode structure102 and gate electrode structure 108 are the same material ormaterial(s). In other embodiments, gate electrode structure 102 has adifferent composition than gate electrode structure 108. Similarly, insome embodiments, gate dielectric layer 103 and gate dielectric layer107 are the same material or material(s) while in other embodiments,they have different compositions. Furthermore, gate electrode structure102 and gate electrode structure 108 may be integrated such that thesame control (e.g., control signal, switching signal, bias, etc.) isprovided via they may be separate such that different control isprovided by gate electrode structure 102 with respect to gate electrodestructure 108. In an embodiment, gate electrode structure 102 mayprovide a body potential to control VT while gate electrode structure108 switches the on/off state of thin film transistor structure 100. Insuch embodiments, gate dielectric layer 103 may be advantageouslythicker than gate dielectric layer 107. For example, gate dielectriclayer 103 may be not less than 30% thicker than gate dielectric layer107. Such integrated or separate control via gate electrode structures102, 108 may be provided via circuitry (not shown) such as metalinterconnect structures.

Thin film transistor structure 100 includes a non-planar or trench-typeTFT structure as illustrated with respect to non-planar semiconductorlayer 105. Such structures provide for provide improved density withrespect to planar TFT structures and improved performance as devicedensity increases. As shown, non-planar semiconductor layer 105 includesa portion 121 that is immediately adjacent to and conformal to gatedielectric layer 103. For example, portion 121 is co-planar with gatedielectric layer 103 such that it extends laterally along gatedielectric layer 103. Non-planar semiconductor layer 105 also includesportions 122, 123 that are along sidewalls 124, 125 of a trench (notlabeled in FIG. 1A) of patterned layer 104. As shown, in someembodiments, portions 122, 123 may extend substantially orthogonallywith respect to portion 121. In some embodiments, portions 122, 123extend outwardly from portion 121 such that the trench is at leastpartially dished. In an embodiment, non-planar semiconductor layer 105has, from a cross-sectional perspective, a substantially U-shapedstructure. In an embodiment, non-planar semiconductor layer 105 has aconcave shape. For example, non-planar semiconductor layer 105 and theportions thereof are substantially conformal to a trench defined by asurface 128 of gate dielectric layer 103 and sidewalls 124, 125 ofpatterned layer 104 and to plateaus 129, 130 of patterned layer 104. Asused herein, the term conformal indicates a layer conforms to anunderling structure although the conformity may be at the same ordiffering thicknesses of the layer across the conforming are. Althoughpatterned layer 104 is illustrated with multiple sidewalls 124, 125,patterned layer 104 may have a single sidewall around the trench.

As shown, gate electrode structure 108 is partially within a trenchformed by non-planar semiconductor layer 105 and by surface 128 andsidewalls 124, 125 as discussed above. For example, gate electrodestructure 108 includes a portion 131 within a trench defined by surface128 and sidewalls 124, 125 such that portion 131 is between sidewalls124, 125 and below plateaus 129, 130. Furthermore, at least a portion ofgate electrode structure 108 (including portion 131) is laterallybetween portions 126, 127 and portions 122, 123 of non-planarsemiconductor layer 105. As shown, gate electrode structure 108 extendsto proximal of portion 121 of non-planar semiconductor layer 105 suchthat gate electrode structure 108 may apply an electric field to portion121 when a bias is applied thereto. Gate dielectric layer 107 is betweengate electrode structure 108 and portion 121 and on sidewalls of gateelectrode structure 108 (e.g., between sidewall spacer 106 and gateelectrode structure 108).

Sidewall spacer 106 is between various portions of non-planarsemiconductor layer 105 and gate dielectric layer 107 and between source109 and gate dielectric layer 107 as well as between drain 110 and gatedielectric layer 107. Sidewall spacer 106 may include any suitabledielectric material and sidewall spacer 106 reduces capacitance couplingfrom source 109 and drain 110 to gate electrode structure 108. As shown,a portion of sidewall spacer 106 extends over portion 126 of non-planarsemiconductor layer 105 and another portion of sidewall spacer 106extends over portion 127 of non-planar semiconductor layer 105.Furthermore, as shown, a bottom of sidewall spacer 106 extends toportion 121 of non-planar semiconductor layer 105. In an embodiment,sidewall spacer 106 is not employed.

Source 109 and drain 110 are coupled to non-planar semiconductor layer105 via portions 126, 127, respectively. In some embodiments, source 109and drain 110 are on non-planar semiconductor layer 105 and, in otherembodiments, an intervening layer is provided therebetween.

Substrate 101 may be any suitable material or materials. In someembodiments, substrate 101 includes a semiconductor material such asmonocrystalline silicon substrate, a silicon on insulator, or the like.In some embodiments, substrate 101 include metallization interconnectlayers for integrated circuits or electronic devices such astransistors, memories, capacitors, resistors, optoelectronic devices,switches, or any other active or passive electronic devices separated byan electrically insulating layer, for example, an interlayer dielectric,a trench insulation layer, or the like. In an embodiment, substrate 101includes underlying layers and devices discussed with respect to FIG.23. In an embodiment, a top surface or layer of substrate 101 includes adielectric material for isolation and interconnect (e.g., metallization)routing to gate electrode structure 108.

Gate electrode structures 102, 108 may be any suitable material ormaterials. Gate electrode structures 102, 108 may include at least oneP-type work function metal or N-type work function metal, depending onwhether the thin film transistor structure 100 is to be included in aP-type metal oxide semiconductor (PMOS) transistor or an N-type metaloxide semiconductor (NMOS) transistor. For a PMOS transistor, metalsthat may be used for the gate electrode structures 102, 108 include, butare not limited to, ruthenium, palladium, platinum, cobalt, nickel, andconductive metal oxides (e.g., ruthenium oxide). Such materials may beprovided individually or in combination. For an NMOS transistor, metalsthat may be used for the gate electrode structures 102, 108 include, butare not limited to, hafnium, zirconium, titanium, tantalum, aluminum,alloys of these metals, and carbides of these metals (e.g., hafniumcarbide, zirconium carbide, titanium carbide, tantalum carbide, andaluminum carbide). In some embodiments, the gate electrode structures102, 108 be a stack of two or more metal layers such that one or moremetal layers are work function metal layers and at least one metal layeris a fill metal layer. Further metal layers may be included for otherpurposes, such as to act as a barrier layer. As discussed, in someembodiments, gate electrode structures 102, 108 are the same material(s)while in other embodiments they have different material(s).

Furthermore, gate dielectric layers 103, 107 may be any suitabledielectric material or materials. In some embodiments, gate dielectriclayers 103, 107 are high-k dielectric material layers having dielectricconstants of not less than that of silicon dioxide. The high-kdielectric material may include elements such as hafnium, silicon,oxygen, titanium, tantalum, lanthanum, aluminum, zirconium, barium,strontium, yttrium, lead, scandium, niobium, and zinc. Examples ofhigh-k materials that may be used in the gate dielectric layers 103, 107include, but are not limited to, hafnium oxide, hafnium silicon oxide,lanthanum oxide, lanthanum aluminum oxide, zirconium oxide, zirconiumsilicon oxide, tantalum oxide, titanium oxide, barium strontium titaniumoxide, barium titanium oxide, strontium titanium oxide, yttrium oxide,aluminum oxide, tantalum oxide, tantalum silicon oxide, lead scandiumtantalum oxide, and lead zinc niobate.

Gate dielectric layers 103, 107 may have any suitable thickness such asthicknesses in the range of 0.5 to 5 nm. In some embodiments, gatedielectric layers 103, 107 are the same material(s) while in otherembodiments they have different material(s).

As discussed, thin film transistor structure 100 employs non-planarsemiconductor layer 105. Thin film transistor structure 100 performancedepends on the composition of the semiconductor employed as non-planarsemiconductor layer 105. Thin film transistor structure 100 may includeany applicable thin film semiconductor material, including traditionalgroup IV semiconductor materials such as silicon (Si), germanium (Ge),and SiGe alloys. In some embodiments, non-planar semiconductor layer 105is crystalline (e.g., a single crystal) SI, Ge, or SiGe. In otherembodiments, thin film transistor structure 100 may include III-Vsemiconductor materials. In some embodiments, non-planar semiconductorlayer 105 is a crystalline (e.g., a single crystal) III-V semiconductorsuch as gallium nitride (GaN), indium gallium arsenic (InGaAs), etc.Furthermore, thin film transistor structure 100 may include amorphous(e.g., having no structural order) or polycrystalline (e.g., havingmicro-scale to nano-scale crystal grains) semiconductor materialsincluding those discussed above. In some embodiments, non-planarsemiconductor layer 105 is amorphous or polycrystalline Si, Ge, SiGe,III-V semiconductor, GaN, or InGaAs.

In some embodiments, non-planar semiconductor layer 105 employs an oxidesemiconductor. An oxide semiconductor is a semiconducting oxide, or asemiconductor comprising oxygen. For such embodiments, a wide band gapoxide channel material offers low leakage. Semiconducting propertiesvary with the oxide semiconductor composition and microstructure. Anoxide semiconductor thin film can be amorphous (e.g.., having nostructural order) or polycrystalline (e.g.., having micro-scale tonano-scale crystal grains)

Examples of oxide semiconductors for use in non-planar semiconductorlayer 105 include metal oxides with a transition metal (e.g., IUPACgroup 4-10) or post-transition metal (e.g.,

IUPAC groups 11-15). In some embodiments, the metal oxide includes atleast one of Mg, Cu, Zn, Sn, Ti, Ni, Ga, In, Sb, Sr, Cr, Co, V, or Mo.The metal oxides may be suboxides (A₂O), monoxides (AO), binary oxides(AO₂), ternary oxides (ABO₃), and mixtures thereof. Non-planarsemiconductor layer 105 may be a p-type, n-type, or intrinsic material.In some embodiments, non-planar semiconductor layer 105 is n-type as anumber of oxide semiconductors have been found to be capable ofsignificant electron densities. Some oxide semiconductors have also beenfound to be capable of significant electron hole densities. Many oxidesemiconductors have high defect density nearer the valence band butdisplay good n-type electrical properties. Some oxide semiconductorshave high defect density in the conduction band but display good p-typeelectrical properties. In some embodiments, non-planar semiconductorlayer 105 is or includes a tin oxide (SnO_(x)), such as Tin (IV) oxide,or SnO₂. In other embodiments, the tin oxide is Tin (II) oxide (SnO) ora mixture of SnO and SnO₂, where x may range between 1 and 2. In someembodiments, non-planar semiconductor layer 105 comprises a zinc oxide(ZnO_(x)), such as Zn(II) oxide, or ZnO. In other embodiments, the zincoxide is zinc dioxide (ZnO₂) or a mixture of ZnO and ZnO₂, where x mayrange between 1 and 2. In some other embodiments, non-planarsemiconductor layer 105 comprises titanium oxide (TiO_(x)), or SnO_(x).Exemplary oxide semiconductors that may have suitable p-typeconductivity include copper oxide (CuO_(x)). In some CuO_(x)embodiments, non-planar semiconductor layer 105 is Cu(I) oxide, or Cu₂O.In other embodiments, non-planar semiconductor layer 105 is Cu(II) oxide(CuO) or a mixture of CuO and Cu₂O, where x may range between 0.5 and 1.Still other exemplary oxide semiconductor compositions include NiO_(x).Any dopants, such as Al, may also be added to any of these metal oxides,such as ZnO.

Non-planar semiconductor layer 105, or various portions thereof, may beintentionally doped, or not. Compared to intrinsic oxide semiconductorsthat are not intentionally doped, n-type and p-type oxide semiconductorsmay have a higher concentration of impurities, such as, but not limitedto, one or more group III element, group V element, and/or elementalhydrogen (H), and/or oxygen vacancies. Dopant levels in non-planarsemiconductor layer 105 may be selected to arrive at an optimalthreshold voltage associated with gating the oxide semiconductor withinthe channel and/or for lowest bulk and/or junction resistance within thesource/drain region. In embodiments where non-planar semiconductor layer105 comprises ZnO_(x), the dopants may include In and Ga. In anembodiment, non-planar semiconductor layer 105 is InGaO₃(ZnO)₅ (e.g.,IGZO).

Source 109 and drain 110 couple to non-planar semiconductor layer 105and provide a contact to routing of metallization layers and othercircuitry. Source 209 and drain 210 may be characterized as a sourceelectrode and a drain electrode, respectively. Source 109 and drain 110may include any suitable material or materials. In some embodiments,source 109 and drain 110 includes one or more of a titanium film and analuminum film. Sidewall spacer 106 may include any suitable dielectricmaterial. For example, sidewall spacer 106 may have any compositionknown to be suitable for electrical isolation, such as, but not limitedto, materials including silicon and oxygen (SiO), materials includingsilicon and nitrogen (SiN), materials including silicon, oxygen, andnitrogen (SiON), low-k materials including a dopant (e.g., SiOF, SiOC),organosilicates, HSQ, MSQ, etc. Patterned layer 104 may include anysuitable dielectric material. For example, patterned layer 104 may haveany composition known to be suitable for electrical isolation, such as,but not limited to, materials including silicon and oxygen (SiO),materials including silicon and nitrogen (SiN), materials includingsilicon, oxygen, and nitrogen (SiON), low-k materials including a dopant(e.g., SiOF, SiOC), organosilicates, HSQ, MSQ, etc. High-k materials(e.g., metal oxides) such as those reference with respect to gatedielectric layers 103, 107 may also be employed as sidewall spacer 106and patterned layer 104. In an embodiment, thin film transistorstructure 100 is within a field oxide, polymeric sacrificial lightabsorbing materials, or the like as discussed further herein.

As discussed, the architecture of thin film transistor structure 100offers the advantages of a trench-type TFT (e.g., improved density withrespect to planar TFT structures) and dual gate control (e.g., bettershort channel control, low contact resistance, and low parasitic gate tosource/drain capacitance). In particular, thin film transistor structure100 provides reduced capacitance from source/drain to gate due tosidewall spacer 106.

FIG. 2A illustrates a cross-sectional view of another example thin filmtransistor structure 200 and FIG. 2B is a top-down view of thin filmtransistor structure 200, arranged in accordance with at least someimplementations of the present disclosure. As shown, FIG. 2A provides across-sectional view along an x-z plane and FIG. 2B provides a top-downview along the A-plane in FIG. 12A (e.g., along an x-y plane). Asillustrated, the x-y plane may be in-plane, in-line, or the like withrespect to a lateral direction of thin film transistor structure 200 andthe z-direction may be perpendicular with respect to the lateraldirection of thin film transistor structure 200.

As shown, thin film transistor structure 200 may include substrate 101,gate electrode structure 102, gate dielectric layer 103, patterned layer104, non-planar semiconductor layer 105, gate dielectric layer 107, gateelectrode structure 108, a source 209, and a drain 210. Source 209 anddrain 210 may be characterized as a source electrode and a drainelectrode, respectively. Notably, thin film transistor structure 200includes a dual gate architecture similar to that of thin filmtransistor structure 100 without sidewall spacer 106 and having source209 and drain 210 with extended portions 203, 204 respectively.Components of thin film transistor structure 200 having the samereference numerals may have any of the characteristics (e.g.,orientations, materials, etc.) as those illustrated and discussed withrespect to thin film transistor structure 100. Such characteristics willnot be repeated for the sake of brevity and clarity of presentation.

Thin film transistor structure 200 includes a source 209 and a drain210. As shown, source 209 includes a portion 203 between portions 122,126 of non-planar semiconductor layer 105 and, similarly, drain 210includes a portion 204 between portions 123, 127 of non-planarsemiconductor layer 105. Furthermore, portion 203 of source 209 extendsto contact portion 121 of non-planar semiconductor layer 105 and portion204 of drain 210 extends to contact portion 121 of non-planarsemiconductor layer 105. Such an architecture provides for source 209and drain 210 (e.g., source and drain metals) adjacent to the portions203, 204 of non-planar semiconductor layer 105 (e.g., along sidewalls ofnon-planar semiconductor layer 105), which advantageously reducescontact resistance between source 209 and non-planar semiconductor layer105 and between drain 210 and non-planar semiconductor layer 105. Aswith source 109 and drain 110, source 209 and drain 210 couple tonon-planar semiconductor layer 105 and provide a contact to routing ofmetallization layers and other circuitry. Source 209 and drain 210 mayinclude any suitable material or materials. In some embodiments, source109 and drain 110 includes one or more of a titanium film and analuminum film.

FIG. 3 illustrates a flow diagram illustrating an example process 300for fabricating thin film transistor structures, arranged in accordancewith at least some implementations of the present disclosure. Forexample, process 300 may be implemented to fabricate thin filmtransistor structure 100 or any other thin film transistor structurediscussed herein. In the illustrated implementation, process 300 mayinclude one or more operations as illustrated by operations 301-308.However, embodiments herein may include additional operations, certainoperations being omitted, or operations being performed out of the orderprovided. In an embodiment, process 300 may fabricate thin filmtransistor structure 1700 as discussed further herein with respect toFIGS. 4-17.

Process 300 may begin at operation 301, where a substrate may bereceived for processing. The substrate may include any suitablesubstrate such as a silicon wafer or the like. In some embodiments, thesubstrate includes underlying devices or electrical interconnects or thelike. For example, the substrate may include peripheral circuitry,metallization layers, and interlayer dielectric materials as discussedwith respect to FIG. 23.

Processing may continue at operation 302, where a bulk gate electrodematerial, a bulk gate dielectric material, a bulk dielectric material, athin film transistor semiconductor material, and a source/drain materialmay be disposed on the substrate. For example, each material may bedisposed as a layer on the substrate and then each preceding layer. Suchbulk material depositions may be performed using any suitable techniqueor techniques. The gate electrode material may include anycharacteristics discussed with respect to gate electrode structure 102,the gate dielectric material may include any characteristics discussedwith respect to gate dielectric layer 103, the dielectric material mayinclude any characteristics discussed with respect to patterned layer104, the thin film transistor semiconductor material may include anycharacteristics discussed with respect to non-planar semiconductor layer105, and the source/drain material may include any characteristicsdiscussed with respect to gate dielectric layer 107. In an embodiment,such bulk materials or material layers may be disposed over substrate101 as discussed with respect to FIG. 4. As discussed, at operations302, multiple layers are disposed. Such operations may be characterizedas disposition or deposition operations, which may be performedseparately or together.

Processing may continue at operation 303, where the material layersdisposed at operation 302 are patterned and isolated. For example, thematerial layers may be patterned into mesas or the like and isolated forthe formation of thin film transistor structures. The material layersmay be patterned using any suitable technique or techniques such aslithography and etch techniques. Furthermore, the patterned materiallayers may be isolated using any suitable technique or techniques suchas material deposition and planar techniques. The material used toisolate the patterned material layers (and ultimately the thin filmtransistor structures) may be any suitable material or material such aspolymeric sacrificial light absorbing materials. In an embodiment, thematerial layers may be patterned and isolated as discussed with respectto FIGS. 5, 6A, and 6B.

Processing may continue at operation 304, where a trench may bepatterned into some the material layers. For example, the isolatedmaterial layers may be patterned to form a trench therein such that thetrench extends through the source/drain material, the thin filmtransistor semiconductor material, and the dielectric material (whichmay be characterized as a patterned layer) but not through the gatedielectric material (nor the gate electrode material) such that thetrench provides an opening to the gate dielectric material and hassidewalls including the source/drain material, the thin film transistorsemiconductor material, and the dielectric material.

The trench may be formed using any suitable technique or techniques suchas lithography and etch techniques. In an embodiment, the materiallayers may be patterned to form a trench or opening as discussed withrespect to FIGS. 7A, 7B, 8, and 9.

Processing may continue at operation 305, where a thin film transistorsemiconductor material may be grown within the trench and a recess etchmay be performed to provide a non-planar thin film transistorsemiconductor material layer along sidewalls of the patterned layer(e.g., the patterned dielectric material) and the exposed surface of thegate dielectric material within the trench. The thin film transistorsemiconductor material growth may be performed using any suitabletechnique or techniques such as lateral epitaxial overgrowth (LEO)techniques using the exposed portions of the thin film transistorsemiconductor material within the trench as a seed material. Such LEOtechniques may provide thin film transistor semiconductor material alongsidewalls of the patterned layer and the exposed surface of the gatedielectric material within the trench but also along at least portionsof the source/drain material. The thin film transistor semiconductormaterial on the source/drain material may optionally be removed usingrecess etch techniques such as providing a fill material such as anoxide and etching the fill material and the thin film transistorsemiconductor material and subsequently selectively etching the fillmaterial. In an embodiment, the thin film transistor semiconductormaterial growth and recess etch may be performed as discussed withrespect to FIGS. 10, 11, 12, and 13.

Processing may continue at operation 306, where a conformal dielectriclayer may be deposited and directionally etched to form a sidewallspacer along sidewalls of the source/drain materials and the thin filmtransistor semiconductor material within the trench while exposing asurface of the thin film transistor semiconductor material within thetrench. The dielectric spacer layer may be deposited using any suitabletechnique or techniques such as chemical vapor deposition (CVD), plasmaenhanced chemical vapor deposition (PECVD), or physical vapor deposition(PVD). Furthermore, the directional etch may be performed using anysuitable technique or techniques such as dry etch techniques. In anembodiment, sidewall spacers may be formed as discussed with respect toFIGS. 14 and 15.

Processing may continue at operation 307, where a gate dielectricmaterial may be conformally disposed over the exposed source and drainmaterial, the sidewall spacer and the exposed thin film transistorsemiconductor material within the trench and a gate electrode materialmay be disposed over the gate dielectric material. The gate dielectricmaterial may be disposed using any suitable technique or techniques suchas CVD, PECVD, PVD, electroplating, etc. In an embodiment, the gatedielectric material and the gate electrode material may be disposed overthe source and drain material, the sidewall spacer and the thin filmtransistor semiconductor material as discussed with respect to FIG. 16.

Processing may continue at operation 308, where portions of the gatedielectric material and the gate electrode material may be removed toform a TFT structure. For example, the TFT structure may have a discretegate electrode structure having an exposed surface (e.g., for contact bya via or other metallization) such that the other surfaces of the gateelectrode structure have a gate dielectric layer thereon. The portionsof the gate dielectric material and the gate electrode material may beremoved using any suitable technique or techniques such as planarizationtechniques. In an embodiment, the portions of the gate dielectricmaterial and the gate electrode material may be removed as discussedwith respect to FIGS. 17A and 17B.

FIGS. 4, 5, 6A, 7A, 8, 9, 10, 11, 12, 13, 14, 15, 16, and 17A illustratecross-sectional side views of example thin film transistor structures asparticular fabrication operations are performed, arranged in accordancewith at least some implementations of the present disclosure. FIGS. 6B,7B, and 17B illustrate top-down views of the thin film transistorstructures of FIGS. 6A, 7A, and 17A, respectively.

As shown in FIG. 4, thin film transistor (TFT) structure 400 includessubstrate 101, a gate electrode material layer 402, a gate dielectricmaterial layer 403, a dielectric layer 404, a semiconductor layer 405,and a source and drain material layer 406. Thin film transistor (TFT)structure 400 may be fabricated using any suitable technique ortechniques. In an embodiment, substrate 101 is received for processing.Substrate 101 may include any materials, devices, and characteristics asdiscussed herein. In an embodiment, substrate 101 includes peripheralcircuitry, metallization layers, and interlayer dielectric materials,etc. as discussed with respect to FIG. 23.

Gate electrode material layer 402 may be formed over or on substrate 101using any suitable technique or techniques such as CVD, PECVD, PVD,electroplating, etc. Gate electrode material layer 402 may include anysuitable materials and characteristics as discussed with respect to gateelectrode structure 102. Gate dielectric material layer 403 may then beformed over or on gate electrode material layer 402 using any suitabletechnique or techniques such as CVD, PECVD, PVD, etc. Gate dielectricmaterial layer 403 may include any suitable materials andcharacteristics as discussed with respect to gate dielectric layer 103.Subsequently, dielectric layer 404 may be formed over or on gatedielectric material layer 403 using any suitable technique or techniquessuch as CVD, PECVD, PVD, etc. Dielectric layer 404 may include anysuitable materials and characteristics as discussed with respect topatterned layer 104. Next, semiconductor layer 405 is formed over or ondielectric layer 404 using any suitable technique or techniques such asmetal-organic chemical vapor deposition (MOCVD), vapor phase epitaxy(VPE), hydride vapor phase epitaxy (HYPE), molecular beam epitaxy (MBE),CVD, PECVD, PVD, etc. In some embodiments, layer transfer techniques maybe used to form semiconductor layer 405 of a monocrystalline material.Semiconductor layer 405 may include any materials and characteristics asdiscussed with respect to non-planar semiconductor layer 105. Finally,source and drain material layer 406 (e.g., a metal layer) is formed overor on semiconductor layer 405 using any suitable technique or techniquessuch as CVD, PECVD, PVD, electroplating, etc. Source and drain materiallayer 406 may include any suitable materials and characteristics asdiscussed with respect to source 109 and drain 110 and/or source 209 anddrain 210. In an embodiment, the component layers are provided as bulklayers over an entirety (or substantially and entirety) of substrate101.

FIG. 5 illustrates a TFT structure 500 similar to TFT structure 400,after the formation of a patterned layer 501 on source and drainmaterial layer 406 and subsequent patterning to form a gate electrodematerial layer 502, a gate dielectric material layer 503, a dielectriclayer 504, a semiconductor layer 505, and a source and drain materiallayer 506, which may be characterized as patterned layers or the like.Patterned layer 501 may be formed using any suitable technique ortechniques such as photolithography techniques and gate electrodematerial layer 402, gate dielectric material layer 403, dielectric layer404, semiconductor layer 405, and source and drain material layer 406may be patterned to form gate electrode material layer 502, gatedielectric material layer 503, dielectric layer 504, semiconductor layer505, and source and drain material layer 506 using any suitabletechnique or techniques such as etch techniques.

FIGS. 6A and 6B illustrates a TFT structure 600 similar to TFT structure500, after the removal of patterned layer 501 via etch techniques or thelike and after the formation of a field insulator layer 601. Fieldinsulator layer 601 may be or include any suitable electricallyisolating dielectric material such as polymeric sacrificial lightabsorbing materials. Field insulator layer 601 may be formed using anysuitable technique or techniques such as bulk deposition andplanarization techniques. As shown in FIG. 6B, which provides a top-downview along the A-plane in FIG. 6A, field insulator layer 601 maysurround gate electrode material layer 502, gate dielectric materiallayer 503, dielectric layer 504, semiconductor layer 505, and source anddrain material layer 506 such that the surrounded material layersprovide a field or location or the like for the formation of a TFTstructure. In the illustrated embodiments, field insulator layer 601surrounds each TFT structure. In other embodiments, multiple TFTs may beformed within an insulated region such that the multiple TFTs sharenon-planar semiconductor layer 105.

FIGS. 7A and 7B illustrates a TFT structure 700 similar to TFT structure600, after the formation of patterned layer 701 via lithographytechniques or the like. As shown, patterned layer 701 includes anopening 702 that will define a trench or opening to be formed withinsource and drain material layer 506, semiconductor layer 505, anddielectric layer 504 and stopping at gate dielectric material layer 503such that a top surface of gate dielectric material layer 503 defines abottom of the trench or opening. As shown in FIG. 7B, which provides atop-down view along the A-plane in FIG. 7A, patterned layer 701 may befully within source and drain material layer 506 (and the layers below)such that the subsequent trench is isolated within the discussedmaterial layers.

FIG. 8 illustrates a TFT structure 800 similar to TFT structure 600,after the formation of a trench 801. Trench 801 may be formed using anysuitable technique or techniques such as selective etch techniques orthe like. The formation of trench 801 further provides for patternedlayer 104, source 109, and drain 110 as discussed herein. As shown,trench 801 includes a surface 802 (or portion) of gate dielectric layer103 and sidewall(s) 803, which includes a sidewall or sidewalls ofpatterned layer 104, a patterned semiconductor layer 805, and source 109or drain 110. Trench 801 may have any suitable shape from a top-downperspective such as square or rectangular (please see FIG. 7B). Althoughillustrated with orthogonal sidewalls(s) 803, trench 801 may havesidewalls that have an obtuse angle (e.g., an angle in the range of >90°to) 120° with respect to the x-y plan, dished or slightly curved(concave) sidewalls, etc. Furthermore, each sidewall portion ofpatterned layer 104, patterned semiconductor layer 805, and source 109or drain 110 may have differing characteristics due to differingmaterial choices, etch conditions, etc. FIG. 9 illustrates a TFTstructure 900 similar to TFT structure 800, after the removal ofpatterned layer 701 via etch techniques or the like.

FIG. 10 illustrates a TFT structure 1000 similar to TFT structure 900,after the formation of a semiconductor layer structure 1005. As shown,semiconductor layer structure 1005 includes patterned semiconductorlayer 805 and a semiconductor layer portion 1006 with the separationindicated by hatched vertical lines. Semiconductor layer portion 1006may be formed using any suitable technique or techniques such as lateralepitaxial overgrowth techniques. Semiconductor layer portion 1006 mayinclude the same or different material as patterned semiconductor layer805. For example, semiconductor layer portion 1006 may include anymaterials and characteristics as discussed with respect to non-planarsemiconductor layer 105. As shown, semiconductor layer portion 1006 maybegin growth at locations 1009 of patterned semiconductor layer 805 suchthat semiconductor layer portion 1006 may be integral with patternedsemiconductor layer 805. In some embodiments, semiconductor layerportion 1006 includes a monocrystalline material formed frommonocrystalline material seed(s) at location 1009. Furthermore,semiconductor layer portion 1006 may include a portion 1008 over asidewall of source 109, a portion 1007 over a sidewall of drain 110, aportion 1010 integral to over sidewall(s) of patterned layer 104, and aportion 1011 on surface 128 of gate dielectric layer 103 (please referto FIGS. 1A and 2A). In some embodiments, portions 1007, 1008 ofsemiconductor layer structure 1005 may be removed as discussed withrespect to FIGS. 11, 12, and 13. In other embodiments, portions 1007,1008 of semiconductor layer structure 1005 may remain adjacent to drain110 and source 109, respectively. In yet other embodiments, portions1007, 1008 may not be formed due to selective growth of semiconductorlayer portion 1006 on surfaces other than the surfaces of source 109 anddrain 110.

FIG. 11 illustrates a TFT structure 1100 similar to TFT structure 1000,after the formation of fill material 1101. Fill material 1101 mayinclude any suitable material such as an oxide and may be formed usingany suitable technique or techniques such as CVD, PECVD, PVD, etc. FIG.12 illustrates a TFT structure 1200 similar to TFT structure 1100, aftera recess etch to remove portions of fill material 1101 and portions1007, 1008 (please refer to FIG. 10) of semiconductor layer structure1005 and to provide non-planar semiconductor layer 105 as discussedherein and a fill material 1201. The recess etch may be performed usingany suitable technique or techniques such as directional dry etchtechniques. FIG. 13 illustrates a TFT structure 1300 similar to TFTstructure 1200, after the removal of fill material 1201. Fill material1201 may be removed using any suitable technique or techniques such asselective etch techniques.

FIG. 14 illustrates a TFT structure 1400 similar to TFT structure 1300,after the formation of a conformal dielectric layer 1401. Conformaldielectric layer 1401 may include any material or materials discussedherein with respect to sidewall spacer 106. Conformal dielectric layer1401 may be formed using any suitable conformal deposition techniquesuch as CVD, PECVD, PVD, etc. As shown, conformal dielectric layer 1401is conformal to exposed surfaces of field insulator layer 601, source109, drain 110, and non-planar semiconductor layer 105. In anembodiment, conformal dielectric layer 1401 may be used to dopenon-planar semiconductor layer 105 to reduce resistance in non-planarsemiconductor layer 105. For example, a dopant may be provided inconformal dielectric layer 1401 and subsequently driven into non-planarsemiconductor layer 105 via an anneal operation.

FIG. 15 illustrates a TFT structure 1500 similar to TFT structure 1400,after a directional etch of conformal dielectric layer 1401 to formsidewall spacer 106. The directional etch may be performed using anysuitable technique or techniques such as dry etch techniques. Sidewallspacer 106 is on a sidewall 1501 of source 109, a sidewall 1502 of drain110, and a sidewall 1503 (or sidewalls) of non-planar semiconductorlayer 105. Furthermore, the directional etch exposes top surfaces offield insulator layer 601, source 109, and drain 110, and a top surface1505 of portion 121 of non-planar semiconductor layer 105. For example,top surface 1505 may be exposed for the application of gate dielectricand gate electrode (e.g., a gate stack) while sidewall 1503 may becoated with sidewall spacer 106 to lower capacitance to the gateelectrode. In an embodiment, sidewall spacer 106 may be used to dopesidewall portions of non-planar semiconductor layer 105 (e.g., thoseportions of non-planar semiconductor layer 105 in contact with sidewallspacer 106) to reduce resistance of non-planar semiconductor layer 105.For example, a dopant may be provided in conformal dielectric layer 1401and, subsequent to performing the directional etch, such dopants may bedriven from sidewall spacer 106 into non-planar semiconductor layer 105via an anneal operation.

FIG. 16 illustrates a TFT structure 1600 similar to TFT structure 1500,after the formation of a gate dielectric layer 1601 and a gate electrodelayer 1602. Gate dielectric layer 1601 may include any materials andcharacteristics discussed herein with respect to gate dielectric layer107. Gate dielectric layer 1601 may be formed using any suitabletechnique or techniques such as CVD, PECVD, PVD, etc. As shown, gatedielectric layer 1601 may be formed conformally to exposed surfaces offield insulator layer 601, source 109, drain 110, sidewall spacer 106,and non-planar semiconductor layer 105 (e.g., the exposed surface ofportion 121 of non-planar semiconductor layer 105). Furthermore, gateelectrode layer 1602 may be formed over gate dielectric layer 1601 usingany suitable technique or techniques such as CVD, PECVD, PVD, etc. Gateelectrode material layer 1602 may include any suitable materials andcharacteristics as discussed with respect to gate electrode structure108. As shown, gate electrode layer 1602 may fill a trench 1604 of gatedielectric layer 1601 as a fill and cover plateaus 1603 of gatedielectric layer 1601 extending laterally in the x-y plane. Furthermore,portion 1604 of gate electrode layer 1602 is within sidewall spacer 106(e.g., between portions of sidewall spacer 106), between source 109 anddrain 110, and within a trench of non-planar semiconductor layer 105.

FIGS. 17A and 17B illustrates a TFT structure 1700 similar to TFTstructure 1600, after the removal of portions of gate electrode layer1602 and gate dielectric layer 1601 to form gate dielectric layer 107and gate electrode structure 108. The portions of gate electrode layer1602 and gate dielectric layer 1601 may be removed using any suitabletechnique or techniques such as planarization techniques. For example,TFT structure 1700 substantially matches TFT structure 100 andillustrates TFT structure 100 within field insulator layer 601. As shownin FIG. 17B, which provides a top-down view along the A-plane in FIG.17A, gate electrode structure 102, gate dielectric layer 103, patternedlayer 104, non-planar semiconductor layer 105, sidewall spacer 106, gatedielectric layer 107, gate electrode structure 108, source 109, anddrain 110 may be isolated within field insulator layer 601. In theillustrated embodiment, a single TFT is within an opening of fieldinsulator layer 601. In other embodiments multiple TFTs may be within anopening. For example, the multiple TFTs may share a common non-planarsemiconductor layer 105.

FIG. 18 illustrates a flow diagram illustrating an example process 1800for fabricating thin film transistor structures, arranged in accordancewith at least some implementations of the present disclosure. Forexample, process 1800 may be implemented to fabricate thin filmtransistor structure 200 or any other thin film transistor structurediscussed herein. In the illustrated implementation, process 1800 mayinclude one or more operations as illustrated by operations 301-305 and1806-1808. However, embodiments herein may include additionaloperations, certain operations being omitted, or operations beingperformed out of the order provided. In an embodiment, process 1800 mayfabricate thin film transistor structure 2200 as discussed furtherherein with respect to FIGS. 4-13 and 19-22.

Process 1800 may begin at operations 301-305 as discussed with respectto FIG. 3 herein. That is, process 1800 may include operations 301-305.In an embodiment, operations 301-305 may be performed as illustratedwith respect to FIGS. 4, 5, 6A, 6B, 7A, 7B, 8,9,10,11,12, and 13.Process 1800 may begin at operation 1806, where a conformal source anddrain material layer may be deposited and directionally etched to form asource and a drain that each extend along sidewalls of the thin filmtransistor semiconductor material within the trench while exposing asurface of the thin film transistor semiconductor material within thetrench. The source and drain material layer may be deposited using anysuitable technique or techniques such CVD, PECVD, PVD, electroplatingetc. Furthermore, the directional etch may be performed using anysuitable technique or techniques such as dry etch techniques. In anembodiment, extended source and drains may be formed as discussed withrespect to FIGS. 19 and 20.

Processing may continue at operation 1807, where a gate dielectricmaterial may be conformally disposed over the exposed source and drainmaterial and the exposed thin film transistor semiconductor materialwithin the trench and a gate electrode material may be disposed over thegate dielectric material. The gate dielectric material may be disposedusing any suitable technique or techniques such as CVD, PECVD, PVD,electroplating, etc. In an embodiment, the gate dielectric material andthe gate electrode material may be disposed over the source and drainmaterial, the sidewall spacer and the thin film transistor semiconductormaterial as discussed with respect to FIG. 21.

Processing may continue at operation 1808, where portions of the gatedielectric material and the gate electrode material may be removed toform a TFT structure. For example, the TFT structure may have a discretegate electrode structure having an exposed surface (e.g., for contact bya via or other metallization) such that the other surfaces of the gateelectrode structure have a gate dielectric layer thereon. The portionsof the gate dielectric material and the gate electrode material may beremoved using any suitable technique or techniques such as planarizationtechniques. In an embodiment, the portions of the gate dielectricmaterial and the gate electrode material may be removed as discussedwith respect to FIGS. 22A and 22B.

FIGS. 19, 20, 21, and 22A illustrate cross-sectional side views ofexample thin film transistor structures as particular fabricationoperations are performed, arranged in accordance with at least someimplementations of the present disclosure. FIG. 22B illustrates atop-down view of the thin film transistor structure of FIG. 22A.

FIG. 19 illustrates a TFT structure 1900 similar to TFT structure 1300,after the formation of a conformal source and drain material layer 1901.Conformal source and drain material layer 1901 may include any materialor materials discussed herein with respect to source 109, drain 110,source 209, and drain 210. Conformal dielectric layer 1401 may be formedusing any suitable conformal deposition technique such as such as CVD,PECVD, PVD, electroplating, etc. As shown, conformal source and drainmaterial layer 1901 is conformal to exposed surfaces of field insulatorlayer 601, source 109, drain 110, and non-planar semiconductor layer105. In some embodiments, conformal source and drain material layer 1901is the same material as source 109 and drain 110 and, in otherembodiments, conformal source and drain material layer 1901 may have adifferent material.

FIG. 20 illustrates a TFT structure 2000 similar to TFT structure 1900,after a directional etch of source and drain material layer 1901 to formsource 209 and drain 210. The directional etch may be performed usingany suitable technique or techniques such as dry etch techniques. Forexample, the directional etch may be a timed dry etch. Source 209 has aportion on a top surface 2001 of non-planar semiconductor layer 105 (asprovided by source 109) and a portion on sidewall 2003 of non-planarsemiconductor layer 105. Similarly, drain 210 has a portion on a topsurface 2002 of non-planar semiconductor layer 105 (as provided bysource 109) and a portion on sidewall 2004 of non-planar semiconductorlayer 105. The portions on sidewalls 2003, 2004 extend to contactportion 121 of non-planar semiconductor layer 105. Furthermore, thedirectional etch exposes a top surface 2005 of portion 121 of non-planarsemiconductor layer 105. For example, top surface 2005 may be exposedfor the application of gate dielectric and gate electrode (e.g., a gatestack) while sidewalls 2003, 2004 may be coated with portions of source209 and drain 210, respectively.

FIG. 21 illustrates a TFT structure 2100 similar to TFT structure 2000,after the formation of a gate dielectric layer 2101 and a gate electrodelayer 2102. Gate dielectric layer 2101 may include any materials andcharacteristics discussed herein with respect to gate dielectric layer107. Gate dielectric layer 2101 may be formed using any suitabletechnique or techniques such as CVD, PECVD, PVD, etc. As shown, gatedielectric layer 2101 may be formed conformally to exposed surfaces offield insulator layer 601, source 109, drain 110, sidewall spacer 106,and non-planar semiconductor layer 105 (e.g., the exposed surface ofportion 121 of non-planar semiconductor layer 105). Furthermore, gateelectrode layer 2102 may be formed over gate dielectric layer 2101 usingany suitable technique or techniques such as CVD, PECVD, PVD, etc. Gateelectrode material layer 2102 may include any suitable materials andcharacteristics as discussed with respect to gate electrode structure108. As shown, gate electrode layer 2102 may fill a trench 2104 of gatedielectric layer 2101 as a fill and cover plateaus 2103 of gatedielectric layer 2101 extending laterally in the x-y plane. Furthermore,portion 2104 of gate electrode layer 2102 is within sidewall spacer 106(e.g., between portions of sidewall spacer 106), between source 109 anddrain 110, and within a trench of non-planar semiconductor layer 105.

FIGS. 22A and 22B illustrates a TFT structure 2200 similar to TFTstructure 2100, after the removal of portions of gate electrode layer2102 and gate dielectric layer 2101 to form gate dielectric layer 107and gate electrode structure 108. The portions of gate electrode layer2102 and gate dielectric layer 2101 may be removed using any suitabletechnique or techniques such as planarization techniques. For example,TFT structure 2200 substantially matches TFT structure 200 andillustrates TFT structure 200 within field insulator layer 601. As shownin FIG. 22B, which provides a top-down view along the A-plane in FIG.22A, gate electrode structure 102, gate dielectric layer 103, patternedlayer 104, non-planar semiconductor layer 105, sidewall spacer 106, gatedielectric layer 107, gate electrode structure 108, source 109, anddrain 110 may be isolated within field insulator layer 601. In theillustrated embodiment, a single TFT is within an opening of fieldinsulator layer 601. In other embodiments multiple TFTs may be within anopening. For example, the multiple TFTs may share a common non-planarsemiconductor layer 105.

FIG. 23 illustrates a cross-sectional side view of a memory devicestructure 2300, arranged in accordance with at least someimplementations of the present disclosure. Memory device structure 2300includes an exemplary implementation of a dual gate TFT structure. Forexample, memory device structure 2300 provides an implementation of anintegrated circuit memory device employing a dual gate TFT structure.Although illustrated with respect to thin film transistor structures100, memory device structure 2300 may implement thin film transistorstructure 200, any other thin film transistor structure discussedherein, or combinations thereof. Such thin film transistor structuresmay be characterized as thin film transistors (TFTs). Thecross-sectional view shown in FIG. 1 is along an A-A′ line that passesthrough capacitors coupled to one bitline of a memory array. Memorydevice structure 2300 further illustrates a portion of an IC thatincludes peripheral circuitry 18 over and/or on a substrate 2350.Peripheral circuitry 18 includes a plurality of FETs 181 that employ amonocrystalline semiconductor for at least the channel semiconductor2321. Peripheral circuitry 18 may further include one or more levels ofinterconnect metallization 2309 embedded within interlayer dielectric(ILD) materials 2303. ILDs 2303 may have any composition known to besuitable for electrical isolation of IC metallization, such as, but notlimited to, materials including silicon and oxygen (SiO), materialsincluding silicon and nitrogen (SiN), materials including silicon,oxygen, and nitrogen (SiON), low-k materials including a dopant (e.g.,SiOF, SiOC), organosilicates, HSQ, MSQ, etc. In the exemplary embodimentillustrated, peripheral circuitry 18 includes metal-one (M1), metal-two(M2) and metal-three (M3) interconnect metallization levels.

Thin film transistor structures 100 are located over peripheralcircuitry 18. As shown, one or more of thin film transistor structures100 employ non-planar semiconductor layers 105, dual gates 102, 108 andother features discussed herein, which are not labeled for the sake ofclarity of presentation. A memory cell 2301 is denoted by dot-dashedline. Individual ones of thin film transistor structures 100 areseparated by field insulator layer 601 as discussed herein. Memory cell2301 includes one storage capacitor of capacitor array 20. Such storagecapacitors or portions thereof may be characterized as capacitorstructures. One capacitor terminal that includes metal 2310 iselectrically (e.g., conductively) coupled to a semiconductor terminal(e.g., source) of an individual one of thin film transistor structures100. Individual ones of storage capacitor array 20 are similarly coupledto a terminal of corresponding individual ones of thin film transistorstructures 100. In the illustrative embodiment, each of the storagecapacitors in array 20 has another terminal including a metal portion2311 connected in parallel through another metal portion 2313 routed toa shared circuit node 25. During memory device operation, circuit node25 may be maintained at a reference voltage potential (e.g., ground).Individual ones of thin film transistor structures 100 have anothersemiconductor terminal (e.g., drain) electrically connected (e.g.,conductively) to bitline metal 60. At least one gate electrode structureof thin film transistor structure 100 is connected to a respectivewordline 10. For example, one or both of gate electrode structures 102,108 (please refer to FIGS. 1A and 2A) are coupled to a respectivewordline 10. Hence, memory cell 2301 and the illustrated adjacent memorycells are electrically coupled to one bitline metal 60 with theirrespective select thin film transistor structure 100 further coupled toseparate wordlines 10. Memory cell 2301 may be replicated over any givenbitline length. Wordlines 10 may be connected to corresponding wordlinedrivers (or a similar voltage source) operable to bias the wordlinesbetween a voltage sufficient to turn off a select transistor and avoltage sufficient to turn on a select transistor. For example,wordlines 10 may be coupled to a wordline driver operable to bias thewordline between a negative voltage (e.g., between 0V and −0.5V)sufficient to turn off an n-type transistor, and a positive voltage(e.g., between 0.5V and 2V) sufficient to turn on an n-type transistor.

In some embodiments, bitline metal 60 comprises an interconnectmetallization trace within a metallization level (e.g., M6) immediatelyabove the metallization level (e.g., M5) in which thin film transistorstructures 100 reside. Bitline 60 is illustrated in dashed line as anindication that bitline 60 is behind the plane of the cross-sectionalview illustrated. Bitline 60 metallization trace is what might bevisible if a portion of dielectric 103 flush with the plane of thecross-section was milled out (e.g., with a FIB during a deprocessing).As further shown, via 148 provides electrical connection between bitline60 and semiconductor terminals (e.g., drains) of thin film transistorstructures 100. Source terminals of thin film transistor structures 100are electrically connected through local interconnect metallization 149.Local interconnect metallization 149 is within the same metallizationlevel (e.g., M6) as bitline 60. Local interconnect metallization 149 isadjacent to, but electrically insulated, from bitline 60.

As discussed, local interconnect metallization 149 electricallyinterconnects a first storage capacitor terminal including metal 2310with a source of thin film transistor structure 100. Capacitor metalportion 2311 is separated from capacitor metal 2310 by an interveningcapacitor insulator 2312. Capacitor insulator 2312 may have any suitablerelative permittivity (e.g., high-k such as HfO₂, doped high-k materialsuch as Al or Zr doped HfO₂, etc.). In an embodiment, capacitor metalportion 2311 is continuous with routing metal portion 2313 across atleast all capacitors 20 associated with bitline 60. Capacitor metalportion 2311 may also be continuous across capacitor array 20 associatedmultiple bitlines. Capacitor metal portion 2311 may therefore tie oneside of all capacitors of a memory array to a common plate referencepotential through circuit node 25, implemented for example with anothermetallization level (e.g., M8).

In some embodiments, an intervening metal shield 2319 separateslaterally adjacent capacitors of capacitor array 20. Any number ofinterconnect metallization levels may be employed to route circuit nodesof the memory array to the underlying peripheral circuitry. In anembodiment, the capacitor reference potential at circuit node 25 isrouted down through five metallization levels (e.g., M8-M3) to be inelectrical communication with one or more control circuit employing FETs181. Likewise, bitline 60 is routed down through three metallizationlevels (e.g., M6-M3) to be in electrical communication with one or moresense amplifier employing FETs 181. Wordlines 10 may also be routed downthrough one or more metallization levels (e.g., M4-M3) to be inelectrical communication with one or more wordline driver employing FETs181. As shown in FIG. 23, FETs 181 include a gate terminal 2320separated from channel semiconductor 2321 by a gate dielectric 2302.Channel semiconductor 2321 separates semiconductor terminals 2304(source semiconductor and drain semiconductor). Contact metallization2305 lands on semiconductor terminals 2304 and is separated from gateterminal 2320 by an intervening dielectric spacer 2307. Any materialsand techniques known to be suitable for fabricating FETs may be employedfor forming FETs 181. FETs 181 may be planar or non-planar devices, forexample. In some advantageous embodiments, FETS 181 are finFETs. One ormore semiconductor materials may be employed in FETs 181. As oneexample, FETs 181 employ a surface layer of a substantiallymonocyrstalline substrate 2350. Substrate 2350 may be any material knownto be suitable for the fabrication of MOSFET (CMOS) circuitry, such as,but not limited to, group IV materials (e.g., silicon, germanium, andSiGe).

FIG. 24 illustrates a mobile computing platform and a data servermachine employing memory devices including dual gate trench shaped thinfilm transistors, arranged in accordance with at least someimplementations of the present disclosure. For example, memory device2450 of server machine 2406 may employ thin film transistor structure100, thin film transistor structure 200, any other thin film transistorstructure discussed herein, or combinations thereof. Server machine 2406may be any commercial server, for example including any number ofhigh-performance computing platforms disposed within a rack andnetworked together for electronic data processing, which in theexemplary embodiment includes a packaged monolithic or IC-eDRAM deviceincluding dual gate trench shaped thin film transistors. The mobilecomputing platform 2405 may be any portable device configured for eachof electronic data display, electronic data processing, wirelesselectronic data transmission, or the like. For example, the mobilecomputing platform 2405 may be any of a tablet, a smart phone, laptopcomputer, etc., and may include a display screen (e.g., a capacitive,inductive, resistive, or optical touchscreen), a chip-level orpackage-level integrated system 2410, and a battery 2415.

Disposed within the integrated system 2410, a substrate 2460 includes aneDRAM 2430 and processor circuitry 2440 (e.g., a microprocessor, amulti-core microprocessor, graphics processor, or the like). eDRAM 2430includes 1C-1TFT cells, with each cell including a dual gate trenchshaped TFT 2431 (e.g., thin film transistor structure 100, thin filmtransistor structure 200, any other thin film transistor structurediscussed herein) and a capacitor 2432 as well as peripheral circuitry2420 (e.g., peripheral circuitry 18), for example as described elsewhereherein and, in particular, with respect to FIG. 23. For monolithicembodiments, substrate 2460 is a semiconductor chip. For multi-chipmodule embodiments, substrate 2460 may be any package substrate, or aninterposer. Processor circuitry 2440, or a separate RFIC chip, may befurther coupled to an antenna (not shown) to implement any of a numberof wireless standards or protocols, including but not limited to Wi-Fi(IEEE 2402.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, longterm evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS,CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well as any otherwireless protocols that are designated as 3G, 4G, 5G, and beyond.

FIG. 25 is a functional block diagram of an electronic computing device2500, arranged in accordance with at least some implementations of thepresent disclosure. Electronic computing device 2500 may employ a dualgate trench shaped TFT as discussed herein. Computing device 2500 may befound inside platform 2405 or server machine 2406, for example. Device2500 further includes a motherboard 2502 hosting a number of components,such as, but not limited to, a processor 2504 (e.g., an applicationsprocessor), which may further incorporate interconnect structures (e.g.,line segments with compositional variation) in accordance withembodiments described herein. Processor 2504 may be physically and/orelectrically coupled to motherboard 2502. In some examples, processor2504 includes an integrated circuit die packaged within the processor2504. In general, the term “processor” or “microprocessor” may refer toany device or portion of a device that processes electronic data fromregisters and/or memory to transform that electronic data into otherelectronic data that may be further stored in registers and/or memory.

In various examples, one or more communication chips 2506 may also bephysically and/or electrically coupled to the motherboard 2502. Infurther implementations, communication chips 2506 may be part ofprocessor 2504. Depending on its applications, computing device 2500 mayinclude other components that may or may not be physically andelectrically coupled to motherboard 2502. These other componentsinclude, but are not limited to, volatile memory (e.g., MRAM 2530, DRAM2532), non-volatile memory (e.g., ROM 2535), flash memory, a graphicsprocessor 2522, a digital signal processor, a crypto processor, achipset 2512, an antenna 2525, touchscreen display 2515, touchscreencontroller 2575, battery 2510, audio codec, video codec, power amplifier2521, global positioning system (GPS) device 2540, compass 2545,accelerometer, gyroscope, audio speaker 2520, camera 2541, and massstorage device (such as hard disk drive, solid-state drive (SSD),compact disk (CD), digital versatile disk (DVD), and so forth), or thelike.

Communication chips 2506 may enable wireless communications for thetransfer of data to and from the computing device 2500. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. Communication chips 2506 may implement anyof a number of wireless standards or protocols, including but notlimited to those described elsewhere herein. As discussed, computingdevice 2500 may include a plurality of communication chips 2506. Forexample, a first communication chip may be dedicated to shorter-rangewireless communications, such as Wi-Fi and Bluetooth, and a secondcommunication chip may be dedicated to longer-range wirelesscommunications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, andothers.

As used in any implementation described herein, the term “module” refersto any combination of software, firmware and/or hardware configured toprovide the functionality described herein. The software may be embodiedas a software package, code and/or instruction set or instructions, and“hardware”, as used in any implementation described herein, may include,for example, singly or in any combination, hardwired circuitry,programmable circuitry, state machine circuitry, and/or firmware thatstores instructions executed by programmable circuitry.

The modules may, collectively or individually, be embodied as circuitrythat forms part of a larger system, for example, an integrated circuit(IC), system on-chip (SoC), and so forth.

While certain features set forth herein have been described withreference to various implementations, this description is not intendedto be construed in a limiting sense. Hence, various modifications of theimplementations described herein, as well as other implementations,which are apparent to persons skilled in the art to which the presentdisclosure pertains are deemed to lie within the spirit and scope of thepresent disclosure.

It will be recognized that the invention is not limited to theembodiments so described but can be practiced with modification andalteration without departing from the scope of the appended claims. Forexample, the above embodiments may include specific combination offeatures. However, the above embodiments are not limited in this regardand, in various implementations, the above embodiments may include theundertaking only a subset of such features, undertaking a differentorder of such features, undertaking a different combination of suchfeatures, and/or undertaking additional features than those featuresexplicitly listed. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A thin film transistor structure comprising: anon-planar layer having a first portion over a first gate dielectriclayer and a second portion conformal to one or more sidewalls of atrench within a patterned layer, wherein the patterned layer is adjacentto the first gate dielectric layer and the non-planar layer comprises asemiconductor material; a first gate electrode structure adjacent to thefirst gate dielectric layer and opposite the first portion of thenon-planar layer; a second gate electrode structure at least partiallywithin the trench of the patterned layer; a second gate dielectric layerbetween the second gate electrode structure and the first portion of thenon-planar layer; and a source and a drain coupled to the non-planarlayer.
 2. The thin film transistor structure of claim 1, wherein thenon-planar layer comprises a third portion over a first plateau of thepatterned layer and a fourth portion over a second plateau of thepatterned layer, wherein the first and second plateaus are each adjacentto the trench and the source and the drain are over the third and fourthportions of the non-planar layer, respectively.
 3. The thin filmtransistor structure of claim 1, wherein a portion of the patternedlayer is on a first portion of the first gate dielectric layer and thenon-planar layer is conformal to a surface of a second portion of thefirst gate dielectric layer within the trench.
 4. The thin filmtransistor structure of claim 1, wherein the second gate dielectriclayer comprises a portion that extends along a sidewall of the secondgate electrode structure within the trench.
 5. The thin film transistorstructure of claim 4, further comprising: a dielectric spacer layerbetween the second portion of the non-planar layer and the portion ofthe second gate dielectric layer.
 6. The thin film transistor structureof claim 5, wherein the non-planar layer comprises a third portionadjacent to the second portion, the third portion of the non-planarlayer is over a plateau of the patterned layer, the source or the drainis over the third portion of the non-planar layer, and the source or thedrain are not in contact with the second portion of the non-planarlayer.
 7. The thin film transistor structure of claim 4, wherein thesource or the drain comprises a portion between the second portion ofthe non-planar layer and the portion of the second gate dielectriclayer.
 8. The thin film transistor structure of claim 7, wherein theportion of the source or the drain is in contact with the first andsecond portions of the non-planar layer.
 9. The thin film transistorstructure of claim 1, wherein the non-planar layer comprises anamorphous or polycrystalline semiconductor material.
 10. The thin filmtransistor structure of claim 1, wherein the first and second gateelectrode structures comprises different materials.
 11. An integratedcircuit (IC) memory device comprising: peripheral circuitry comprising aplurality of field effect transistors (FETs), wherein individual ones ofthe FETs comprise a monocrystalline semiconductor channel; and a memorycell array monolithically integrated with the peripheral circuitry, thememory cell array comprising a plurality of capacitor structures coupledto a plurality of thin film transistors (TFTs), wherein individual onesof the TFTs comprise: a non-planar layer having a first portion over afirst gate dielectric layer and a second portion conformal to one ormore sidewalls of a trench of a patterned layer adjacent to the firstgate dielectric layer, the non-planar layer comprising a semiconductormaterial; a first gate electrode structure adjacent to the first gatedielectric layer and opposite the first portion of the non-planar layer;a second gate electrode structure at least partially within the trenchof the patterned layer; a second gate dielectric layer between thesecond gate electrode structure and the first portion of the non-planarlayer; and a source and a drain coupled to the non-planar layer.
 12. TheIC memory device of claim 11, wherein the non-planar layer comprises athird portion over a first plateau of the patterned layer and a fourthportion over a second plateau of the patterned layer, wherein the firstand second plateaus are each adjacent to the trench and the source andthe drain are over the third and fourth portions of the non-planarlayer, respectively.
 13. The IC memory device of claim 11, wherein thesecond gate dielectric layer comprises a portion that extends along asidewall of the second gate electrode structure within the trench, theIC memory device further comprising: a dielectric spacer layer betweenthe second portion of the non-planar layer and the portion of the secondgate dielectric layer.
 14. The IC memory device of claim 13, wherein thenon-planar layer comprises a third portion adjacent to the secondportion, the third portion of the non-planar layer is over a plateau ofthe patterned layer, the source or the drain is over the third portionof the non-planar layer, and the source or the drain are not in contactwith the second portion of the non-planar layer.
 15. The IC memorydevice of claim 11, wherein the second gate dielectric layer comprises aportion that extends along a sidewall of the second gate electrodestructure within the trench, wherein the source or the drain comprises aportion between the second portion of the non-planar layer and theportion of the second gate dielectric layer.
 16. The IC memory device ofclaim 15, wherein the portion of the source or the drain is in contactwith the first and second portions of the non-planar layer.
 17. A methodof fabricating a thin film transistor structure comprising: forming atrench extending through a source and drain material layer, a first thinfilm semiconductor layer, and a dielectric layer to expose a surface ofa first gate dielectric layer, wherein the first gate dielectric layeris over a first gate electrode structure; growing a second thin filmsemiconductor layer from the first thin film semiconductor layer andover the dielectric layer and the surface of the first gate dielectriclayer to form a non-planar thin film semiconductor layer having aportion over the surface of the first gate dielectric layer; disposing asecond gate dielectric layer over the portion of the non-planar thinfilm semiconductor layer; and disposing a second gate electrodestructure at least partially within the trench, wherein the second gatedielectric layer is between the portion of the non-planar thin filmsemiconductor layer and the second gate electrode structure.
 18. Themethod of claim 17, wherein the second gate dielectric layer comprises aportion that extends along a sidewall of the second gate electrodestructure within the trench.
 19. The method of claim 17, furthercomprising: disposing a dielectric spacer layer on a sidewall portion ofthe non-planar thin film semiconductor layer, wherein disposing thesecond gate dielectric layer comprises disposing the second gatedielectric layer on at least a sidewall of the dielectric spacer layer.20. The method of claim 17, further comprising: disposing a secondsource and drain material layer on a sidewall portion of the non-planarthin film semiconductor layer and the portion of the non-planar thinfilm semiconductor layer; and removing at least a portion of the secondsource and drain material layer to expose the portion of the non-planarthin film semiconductor layer, wherein disposing the second gatedielectric layer comprises disposing the second gate dielectric layer onat least a sidewall of the second source and drain material layer. 21.The method of claim 17, wherein growing the second thin filmsemiconductor layer from the first thin film semiconductor layercomprises growing a portion of the second thin film semiconductor layerover at least a portion of an exposed surface of the source and drainmaterial layer, the method further comprising: providing a bulk materialover the first and second thin film semiconductor layers; performing arecess etch to remove the portion of the second thin film semiconductorlayer over the exposed surface of the source and drain material layer;and removing remaining portions of the bulk material.